1. Field of the Invention
This invention relates to the art of printing and in particular to ink rollers.
2. Brief Description of the Prior Art
The following U.S. patents are made of record: U.S. Pat. Nos. 3,783,083; 3,954,545; 4,207,818; and 6,234,078.
As shown, for example, in U.S. Pat. No. 3,783,083 it is known to provide an ink roller which rolls over a print head to ink its printing characters. The ink roller typically includes a sleeve-mounting base with a circular-cylindrical outer surface. A tubular, porous, resilient, inked sleeve is received about the base and has an inner surface in supported contact in the outer surface of the base. In order to keep the sleeve from rotating or slipping relative to the base during inking of the print head, the inside diameter of the inked sleeve is made smaller than the outside diameter of the base. The sleeve is stretched over the base and consequently the sleeve is under hoop tension. Accordingly, the sleeve grips the base and rotation of the sleeve and the base relative to each other is prevented. This, however, causes the ink-containing cells of the porous sleeve to be compressed or squeezed. Cell compression is most prevalent at or near the inside surface of the sleeve and becomes progressively less as the distance from the axis of the sleeve increases. However, cell compression can occur throughout the sleeve. The effect of cell compression is to force or squeeze the ink-containing cells or pores, which forces ink out of these pores. The ink that was squeezed out migrates toward the outer surface of the sleeve. This causes overinking of the print head particularly when the ink roller is new. The printer will print indicia on a surface, such as the surface of a label, with an excessive amount of ink until such time as the excess ink is depleted. Not only does this give the printed indicia a poor appearance and can lead to smearing of the excess ink following printing but the useful or operational life of the ink roller is shortened because the compressed cells will have been depleted prematurely. This excess ink also has a tendency to be deposited on the inside of the ink roller packaging, giving an unsightly appearance, and at the same time increasing the likelihood that the user of the ink roller will get ink on his/her hands. In that ink is an expensive part of the cost of an ink roller, it is important to avoid such ink wastage. In a typical prior art ink roller the outside diameter of the base was 3.934 mm, the inside diameter of the inked sleeve was 3.173 mm, and the outside diameter of the inked sleeve was 10.914 mm and consequently substantial compression of the cells occurred.